While a number of recent efforts are being made to achieve a finer pattern rule in the drive for higher integration and operating speeds in LSI devices, deep-ultraviolet lithography is thought to hold particular promise as the next generation in microfabrication technology. In particular, photolithography using a KrF or ArF excimer laser as the light source is strongly desired to reach the practical level as the micropatterning technique capable of achieving a feature size of 0.3 μm or less.
The chemically amplified resist materials for use in photolithography using light of an excimer laser, especially ArF excimer laser having a wavelength of 193 nm, are, of course, required to have a high transparency to light of that wavelength. In addition, they are required to have an etching resistance sufficient to allow for film thickness reduction, a high sensitivity sufficient to eliminate any extra burden on the expensive optical material, and especially, a high resolution sufficient to form a precise micropattern. To meet these requirements, it is crucial to develop a base resin having a high transparency, dry etch resistance and reactivity. Active efforts have been made to develop such base resins.
Known high transparency resins include copolymers of acrylic or methacrylic acid derivatives (see JP-A 4-39665). These resins, however, are very low in dry etching resistance and not considered practical as the resist composition base resin. Their drawback can be overcome by introducing a certain amount of units containing a polycyclic structure as typified by adamantane structure. However, the resulting polymer becomes highly hydrophobic as a whole, often inviting pattern stripping due to reduced substrate adhesion and development defects due to developer liquid cissing. That is, the introduction of a large amount of polycyclic structure, which is intended to enhance etch resistance, is impractical because of the occurrence of pattern stripping and development defects. On the other hand, the introduction of a small amount of polycyclic structure results in practically unacceptable etch resistance. While a finer pattern rule is being demanded, there is a need to have a polymer for resist material which exerts satisfactory performance with respect to sensitivity and resolution, has practically acceptable etching resistance, good adhesion to substrates and affinity to liquid developers.